quant_tool_int8 量化时出现Tengine plugin device CPU is unregistered.

[zhangliming0113]

1. 量化工具cmake配置：cmake -DTENGINE_BUILD_CONVERT_TOOL=ON -DTENGINE_BUILD_QUANT_TOOL=ON -DTENGINE_BUILD_EXAMPLES=OFF -DTENGINE_ENABLE_ACL=ON ..
2. onnx转tmfile以及quant_tool_uint8量化均正常，但quant_tool_int8时提示Tengine plugin device CPU is unregistered. 不过I8模型生成了，使用时create graph fail